Point-to-multipoint passive optical network that utilizes variable-length packets

1. A point-to-multipoint optical communications system comprising: an optical line terminal (OLT); and a plurality of optical network units (ONUs) connected to said OLT by a passive optical network in which downstream data is transmitted from said OLT to said ONUs over said passive optical network and upstream data is transmitted from said ONUs to said OLT over said passive optical network: said OLT transmitting downstream data over said passive optical network in variable-length downstream packets; said ONUs transmitting downstream data over said passive optical network within ONU-specific time slots utilizing time division multiplexing, wherein said ONU-specific time slots are filled with multiple variable-length upstream packets; said OLT includes: a fragment buffer for storing packet fragments that have been transmitted upstream from said ONUs; and fragment logic for: identifying said end-of-packet-fragment code of said first packet fragment; buffering said first packed fragment in said OLT fragment buffer; identifying said start-of-packet-fragment code of said first packet fragment; reconstructing said variable-length upstream packet from said first and second packet fragments; said ONUs include: fragment buffers for storing packet fragments that are to be transmitted upstream from said ONUs; and fragment logic for: splitting a variable-length upstream packet into first and second packet fragments; and adding an end-of-packet-fragment code to said first packet fragment and adding a start-of-packet-fragment code to said second packet fragment.

2. The system of claim 1 wherein said variable-length downstream packets are formatted according to IEEE 802.3.

3. The system of claim 1 wherein said variable-length downstream packets include Internet protocol (IP) datagrams.

4. The system of claim 3 wherein the lengths of said variable-length downstream packets include the lengths of said IP datagrams plus packet overhead.

5. The system of claim 1 wherein said variable-length upstream packets include Internet protocol (IP) datagrams.

6. The system of claim 5 wherein the lengths of said variable-length upstream packets include the lengths of said IP datagrams plus packet overhead.

7. The system of claim 1 wherein: said variable-length downstream packets and said variable-length upstream packets are formatted according to IEEE 802.3; and said downstream data and said upstream data include Internet protocol (IP) datagrams.

8. A method for exchanging information between an optical line terminal (OLT) and mutliple optical network units (ONUs) in a point-to-multipoint passive optical network comprising: transmitting downstream data from said OLT to said ONUs in variable-length downstream packets; transmitting upstream data from said ONUs to said OLT in ONU-specific time slots utilizing time division multiplexing to avoid transmission collisions, wherein said ONU-specific time slots are filled with multiple variable-length upstream packets; splitting a variable-length upstream packet into a first packet fragment and a second packet fragment; adding an end-of-packet-fragment code to the end of said first packet fragment; adding a start-of-packet-fragment code to the start of said second packet fragment; transmitting said first packet fragment upstream in a first ONU-specific time slot; buffering said second packet fragment for transmission in a second ONU-specific time slot that is different from said first ONU-specific time slot; buffering said first packet fragment after said first packet fragment is received at said OLT; and reconstructing said variable-length upstream packet, at said OLT, from said first packet fragment and said second packet fragment.

9. The system of claim 8 wherein said variable-length downstream and upstream packets are formatted in accordance with IEEE 802.3 protocol.

10. The method of claim 8 wherein said variable-length downstream and upstream packets include overhead and a payload, and wherein the length of each of said variable-length packets includes the length of an Internet protocol (IP) datagram that is included in the payload of each of said variable-length packets plus the packet overhead.

11. A point-to-multipoint optical communications systems comprising: an optical line terminal (OLT); and a plurality of optical network units (ONUs) connected to said OLT by a passive optical network in which downstream data is transmitted from said OLT to said ONUs and upstream data is transmitted from said ONUs to said OLT; said OLT including means for formatting downstream datagrams into variable-length downstream packets; each of said ONUs including: means for formatting upstream datagrams into variable-length upstream packets: and means for timing the transmission of said variable-length upstream packets to coincide with ONU-specific time slots in order to avoid collisions with upstream packets from other ONUs, wherein said ONU-specific time slots are filled with multiple variable-length upstream packets; said OLT includes: a fragment buffer for storing packet fragments that have been transmitted upstream from said ONUs; fragment logic for: identifying said end-of-packet fragment code of said first packet fragment; buffering said first packet fragment in said OLT fragment buffer; identifying said start-of-packet-fragment code of said second packet fragment; and reconstructing said variable-length upstream packet from said first and second packet fragments; said ONUs include: fragment buffers for storing packet fragments that are to be transmitted upstream from said ONUs; fragment logic for: splitting a variable-length upstream packet into first and second packet fragments; and adding an end-of-packet-fragment code to said first packet fragment and adding a start-of-packet-fragment code to said second packet fragment.

12. The system of claim 11 wherein said variable-length downstream packets are formatted according to IEEE 802.3.

13. The system of claim 11 wherein said downstream datagrams are Internet protocol (IP) datagrams.

14. The system of claim 13 wherein the length of said variable-length downstream packets include the lengths of said IP datagrams plus packet overhead.

15. The system of claim 11 wherein said upstream datagrams are Internet protocol (IP) datagrams.

16. The system of claim 15 wherein the lengths of said variable-length upstream packets include the lengths of said IP datagrams plus packet overhead.

17. The system of claim 11 wherein: said variable-length downstream packets and said variable-length upstream packets are formatted according to IEEE 802.3; and said downstream datagrams and said upstream datagrams are Internet protocol (IP) datagrams.

18. A point-to-multipoint optical communications system comprising: an optical line terminal (OLT); and a plurality of optical network units (ONUs) connected to said OLT by a passive optical network in which downstream data is transmitted from said OLT to said ONUs over said passive optical network and upstream data is transmitted from said ONUs to said OLT over said passive optical network; said OLT transmitting downstream data over said passive optical network in variable-length downstream packets; said ONUs transmitting upstream data over said passive optical network within ONU-specific time slots utilizing time division multiplexing, wherein said ONU-specific time slots are filled with multiple variable-length upstream packets; said OLT including a fragment buffer for storing packet fragments that have been transmitted upstream from said ONUs; said ONUs including; fragment buffers for storing packet fragments that are to be transmitted upstream from said ONUs; fragment logic for splitting a variable-length upstream packet into first and second packet fragments, adding an end-of-packet-fragment code to said first packet fragment, and adding a start-of-packet-fragment code to said second packet fragment; said OLT includes fragment logic for: identifying said end-of-packet-fragment code of said first packet fragment; buffering said first packet fragment in said OLT fragment buffer; identifying said start-of-packet-fragment code of said second packet fragment; and reconstructing said variable-length upstream packet from said first and second packet fragments.

19. The system of claim 18 wherein said variable-length downstream packets are formatted according to IEEE 802.3.

20. The system of claim 18 wherein said variable-length downstream packets included Internet protocol (IP) datagrams.

21. The system of claim 20 wherein the lengths of said variable-length downstream packets include the lengths of said IP datagrams plus packet overhead.

22. The system of claim 18 wherein said variable-length upstream packets are formatted according to IEEE 802.3.

23. The system of claim 18 wherein said variable-length upstream packets include Internet protocol (IP) datagrams.

24. The system of claim 23 wherein the lengths of said variable-length upstream packets include the lengths of said IP datagrams plus packet overhead.

25. The system of claim 18 wherein; said variable-length downstream packets and said variable-length upstream packets are formatted according to IEEE 802.3; and said downstream data and said upstream data include Internet protocol (IP) datagrams.

26. A method of exchanging information between an optical line terminal (OLT) and multiple optical network units (ON Us) in a point-to-multipoint passive optical network comprising: transmitting downstream data from said OLT to said ONUs in variable-length downstream packets; transmitting downstream synchronization markers at constant time intervals; transmitting upstream data from said ONUs to said OLT in ONU-specific time slots utilizing time division multiplexing to avoid transmission collisions, wherein said ONU-specific time slots are filled with variable-length upstream packets; splitting a variable-length upstream packet into a first packet fragment and a second packet fragment; adding an end-of-packet-fragment code to the end of said first packet fragment: adding a start-of-packet-fragment code to the start of said second packet fragment; transmitting said first packet fragment upstream in a first ONU-specific to time slot; buffering said second packet fragment for transmission in a second ONU-specific time slot that is different from said first ONU-specific time slot; buffering said first packet fragment after said first packet fragment is received at said OLT; and reconstructing said variable-length upstream packet, at said OLT, from said first packet fragment and said second packet fragment.

27. The method of claim 26 wherein said variable-length downstream and upstream packets are formatted in accordance with the IEEE 802.3 protocol.

28. The method of claim 26 wherein said variable-length downstream and upstream packets include packet overhead and a payload, and wherein the length of each of said variable-length packets includes the length of an Internet protocol (IP) datagram that is included in the payload of each of said variable-length packets plus the packet overhead.

29. The method of claim 26 wherein said ONU-specific time slots are filled with multiple variable-length packets according to IEEE 802.3 format.

30. A method for exchanging information between an optical line terminal (OLT) and multiple optical network units (ONUs) in a point-to-multipoint passive optical network comprising: transmitting downstream data from said OLT to said ONUs in variable-length downstream packets; transmitting upstream data from said ONUs to said OLT in ONU-specific time slots utilizing time division multiplexing to avoid transmission collisions, wherein said ONU-specific time slots are filled with variable-length upstream packets; splitting a variable-length upstream packet into a first packet fragment and a second packet fragment; adding an end-of-packet-fragment code to the end of said first packet fragment; adding a start-of-packet-fragment code to the start of said second packet fragment; transmitting said first packet fragment upstream in a first ONU-specific time slot; buffering said second packet fragment for transmission in a second ONU specific time slot that is different from said first ONU-specific time slot; buffering said first packet fragment after said first packet fragment is received at said OLT; and reconstructing said variable-length upstream packet, at said OLT from said first packet fragment and said second packet fragment.

31. The method of claim 30 wherein said variable-length downstream and upstream packets are formatted in accordance with the IEEE 802.3 protocol.

32. The method of claim 30 wherein said variable-length downstream and upstream packets include packet overhead and a payload, and wherein the length of each of said variable-length packets includes the length of an Internet protocol (IP) datagram that is included in the payload of each of said variable-length packets plus the packet overhead.

33. A point-to-multipoint optical communications system comprising: an optical line terminal (OLT); and a plurality of optical network units (ONUs) connected to said OLT by a passive optical network in which downstream data is transmitted from said OLT to said ONUs and upstream data is transmitted from said ONUs to said OLT; said OLT including means for formatting downstream datagrams into variable-length downstream packets and a fragment buffer for storing packet fragments that have been transmitted upstream from said ONUs; each of said ONUs including: means for formatting upstream datagrams into variable-length upstream packets; means for timing the transmission of said variable-length upstream packets to coincide with the ONU-specific time slots in order to avoid collisions with upstream packets from other ONUs; fragment buffers for storing packet fragments that are to be transmitted upstream from said ONUs; and fragment logic for: splitting a variable-length upstream packet into first and second packet fragments; and adding an end-of-packet fragment code to said first packet fragment and adding a start-of-packet-fragment code to said second packet fragment; said OLT including fragment logic for: identifying said end-of-packet-fragment code of said first packet fragment; buffering said first packet fragment In said OLT fragment buffer; identifying said start-of-packet-fragment code of said second packet fragment; and reconstructing said variable-length upstream packet from said first and second packet fragments.

34. The system of claim 33 wherein said variable-length downstream packets are formatted according to IEEE 802.3.

35. The system of claim 33 wherein said downstream datagrams are Internet protocol (IP) datagrams.

36. The system of claim 35 wherein the lengths of said variable-length downstream packets include the lengths of said IP datagrams plus packet overhead.

37. The system of claim 33 wherein said variable-length upstream packets are formatted according to IEEE 802.3.

38. The system of claim 33 wherein said upstream datagrams are Internet protocol (IP) datagrams.

39. The system of claim 38 wherein the lengths of said variable-length upstream packets include the lengths of said IP datagrams plus packet overhead.

40. The system of claim 33 wherein: said variable-length downstream packets and said variable-length upstream packets are formatted according to IEEE 802.3; and said downstream datagrams and said upstream datagrams are Internet protocol (IP) datagrams.

41. A point-to-multipoint optical communications system comprising and optical line terminal (OLT); and a plurality of optical network units (ONUs) connected to said OLT by a passive optical network in which downstream data is transmitted from said OLT to said ONUs over said passive optical network and upstream data is transmitted from said ONUs to said OLT over said passive optical network; said OLT transmitting downstream data over said passive optical network in variable-length downstream packets and downstream synchronization markers at constant time intervals; said ONUs transmitting upstream data over said passive optical network within ONU-specific time slots utilizing time division multiplexing, wherein said ONU-specific time slots are filled with multiple variable-length upstream packets, said OLT includes: a fragment buffer for storing packet fragments that have been transmitted upstream from said ONUs; fragment logic for: identifying said end-of-packet fragment code of said first packet fragment; buffering said first packet fragment in said OLT fragment buffer; identifying said start-of-packet-fragment code of said second packet fragment; reconstructing said variable-length upstream packet from said first and second packet fragments; said ONUs include: fragment buffers for storing packet fragments that are to be transmitted upstream from said ONUs; fragment logic for: splitting a variable-length upstream packet into first and second packet fragments; and adding an end-of-packet-fragment code to said first packet fragment and adding a start-of-packet fragment code to said second packet fragment.

42. The system of claim 41 wherein said variable-length downstream packets are formatted according to IEEE 802.3.

43. The system of claim 41 wherein said variable-length downstream packets include Internet protocol (IP) datagrams.

44. The system of claim 43 wherein the lengths of said variable length downstream packets includes the lengths of said IP datagrams plus packet overhead.

45. The system of claim 41 wherein said variable-length upstream packets include Internet protocol (IP) datagrams.

46. The system of claim 45 wherein the lengths of said variable-length upstream packets include the lengths of said IP datagrams plus packet overhead.

47. The system of claim 41 wherein; said variable-length downstream packets and said variable-length upstream packets are formatted according to IEEE 802.3; and said downstream data and said upstream data include Internet protocol (IP) datagrams.